In order to reduce potential danger to the environment, a biohazard laboratory maintains an internal air pressure that is 1% lower than atmospheric pressure. The net force acting on a 1.8-m2 external window of this laboratory due to air pressure is most nearly

1.8 N
18 N
1.8 × 102 N
1.8 × 103 N
1.8 × 104 N

I thought I would just find 1% of atmospheric pressure and this was 1013 (atmospheric pressure is 101300 Pa). From using the P=F/A equation I think the answer is either 1.8e3 or 1.8e4... Can someone help me to ensure my calculations to reach my answer?